If your chickens look healthy, are laying fine, good weight, etc.. I would not worm. If you suspect worms, keep a very close eye on their poo, and see if you find anything--this will tell you what type of worms, and thus, what wormer to use. If you don't see anything, and still suspect worms, you could have a fecal float done to see what is there and what to use. If they have not been wormed, I would be nervous about using a broad-based wormer such as Ivermectin right off the bat, start with Wazine if you don't know what to do, or can't get a fecal float.
I second that. Deworming can be really hard on the chickens. I have a question about this that I've already posted..........I send a composite stool specimen to the vet's once a year, and check for worms. I'm just not sure if the usual fecal test gets all the chicken worms too. But if it does, I think its a great way to test for worms without just treating all of them for no reason.
